I am going to buy one of these for J80 racing and I was wondering if the RS100 class rules would allow it on the RS100? I want to get a compass for the RS100 as well so if it is allowed I could use it on both boats rather than having to buy two separate electronic items.

Here is some of the technical spiel:

Speed and Course Over Ground

Ten seconds after your start, the ProStart automatically switches to showing your speed over ground (GPS speed) and course over ground. The accuracy and responsiveness of the speed measurements make the ProStart an unparalleled tool for optimizing your speed.

Since COG and SOG describe your course over the bottom (where the marks are anchored) the ProStart is also an extremely powerful tool for determining the influence of current on your performance. When you cross a tideline, the numbers on the ProStart jump and you can instantly see how favorable the new current is.

The class rules state that GPS is not allowed during racing so the velocitek can only be used in compass mode. This mode does not always give accurate wind direction information in changing tide conditions your track over the ground will bend and the pasting velocitek will think that the course you are steering will have changed.

Hope this helps rather than confuses the Tacktic compass is what most 100 sailors use.